Paper treating solution of an alphaolefin/maleic anhydride copolymer and a bisulfite



United States Patent PAPER TREATING SOLIiITION OF AN ALPHA-OLEFIN/MALEIC ANHYDRIDE COPOLYMER AND A BISULFITE Charles P. Farley,Florissant, Mo., assignor to Monsanto Company, St. Louis, Mo., acorporation of Delaware No Drawing. Filed Nov. 12, 1964, Ser. No.410,724

6 Claims. (Cl. 260--29.6)

This invention relates to the production of aqueous basic solutions ofsynthetic resins which are especially adapted for use as paper treatmentchemicals, and to paper treated with such solutions. More particularly,this invention provides improved aqueous basic solutions of syntheticresins for treating paper and paper products, paper products treatedwith said improved aqueous basic synthetic resin solutions, andprocesses for improving the color stability of the .synthetic resintreated paper upon oven aging of the paper as is evidenced by the lowerbrightness loss in papers treated with the compositions of thisinvention.

In the past, paper producers have applied to formed paper many differentchemicals in an effort to obtain paper which was more translucent orless opaque so that the paper could be used for various purposes, e.g.,as engineering tracing papers, as reproduction or copy paper and forpackaging purposes. In reproduction systems the need for translucency ortransparency as it is loosely termed in the paper making art, is relatedto the speed of graphic copying by such processes as diazo,thermographic, or silver halide processes in which visual, ultravioletand/or infrared light is passed through the translucent paper to producea copy. The copy may be on a separate sensitized sheet or directly onthe translucent sheet. In packaging applications, the need fortranslucency is to permit viewing of the packaged items by thepurchaser; however, strength and barrier properties must be impartedsimultaneously. The role of the translucentizing chemical therefore mayinvolve considerably more than translucency; for some applications itmay be desirable to impart barrier properties such as resistance topenetration by grease and oil and by vapors and gases. For otherpurposes, papers having good release properties are desired, e.g., forpackaging tacky and pressure sensitive materials such as uncured rubberstocks, and for backings for labels and paper and cloth adhesive tapes.Treated papers of this invention can be used for these purposes.

Most chemicals applied to paper to impart translucency, barrier, and/orrelease properties to the treated paper have previously been appliedfrom non-aqueous solvents which required that the application beaccomplished off the paper making machine in a secondary operation andhence, required more handling of the paper. The use of non-aqueoussolvent techniques is not desira'ble because of flammability or toxicityof the solvent or both. There is a basic market need to produce paperhaving translucency, barrier, and/or release properties on the papermaking machine using conventional equipment.

Water solutions of high molecular weight polymers have been applied topaper. However, high polymer solutions are usually too viscous forefficient application. They do not penetrate the base sheet sufficientlyto reduce the opacity as desired and their use requires slower machinespeed. The opacity of paper and extent of reduction of opacity in agiven paper is spoken of in the TAPPI standard T 425 min terms of acontrast-ratio. This contrast-ratio method of determining the opacity ofpaper is defined as 100 times the ratio of the diffuse reflectance, R ofa specimen backed with a black body of not more than 0.005 reflectance,to the diffuse reflectance, R of the same paper specimen backed with awhite body having an absolute reflectance of 0.89 the reflectance offreshly deposited magnesium oxide; C0.89=(RB/RW). Thus, the contrastratio is 100% for perfectly opaque paper, and is only a few. percent fora perfectly transparent sheet.

Besides lowering the opacity of paper, to be acceptable to the papermaker the given chemical applied to paper must not only penetrate intoand fill up the pores of the paper quickly but it must not substantiallyreduce the good tensile and internal tear strengths, or the foldingendurance of the base sheet. Further, the chemical resin must be onewhich does not migrate from the base sheet to adjacently held absorbentmaterial. It must not cause blocking or sticking together of treatedpaper when it is rolled up or stacked sheet upon sheet. Also the treatedpaper must still be receptive to ink and ink eradicators. The treatedpaper must also" be receptive to pencil marks which can easily be erasedleaving no images. The treated sheet should also be trans lucent tolight in the near ultraviolet and blue region of the light spectrum(actinic region for diazo reproduction systems) and also be translucentto near infrared radiation for use of the treated paper in otherapplications such as the thermographic reproduction methods, arepresentative example of which is the Thermofax technique ofreproduction. The treated paper thus obtained must also be reworkable torecover the broke in the beater.

To obtain treated paper meeting all of these requirements in anefficient and economical manner to be commercially significant isunderstandably a diflicult standard for a paper treatment chemical.

Briefly, this invention provides improved compositions for accomplishingthe above stated objectives. The compositions of this invention may bedescribed as (1) an aqueous solution of an aliphatic alkenealpha-olefin/maleic anhydride copolymer having an olefin to maleicanhydride molar ratio of from about 1:1 to about 1:19 and an averagemolecular weight of from about 1000 to about 10,000, the alpha-olefinshaving from about 6 to about 24 carbon atoms and having dissolvedtherein (2) a minor amount (generally not over about 10%) based on theweight of the polymer solids, of an alkali metal bisulfite or alkalimetal sulfite. The alkali metal of the salt preferably has an atomicweight of from about 22.9 to about 39, that is, it is preferably eithersodium or potassium.

It has been found that when paper is impregnated or coated with themodified aqueous basic copolymer compositions as described above, andthe treated paper thus obtained is dried and aged in an oven in astandard test C. for 72 hours) the color stability of the aged paper isimproved. This discovery is important to paper makers who wish to obtainpapers having improved translucency, barrier properties such as greaseresistance, moisture, vapor and gas resistance, and release properties,which properties may be obtained singly or in combination depending uponthe paper base stock to which the resins are applied, while holding orkeeping as much as possible the original brightness of the untreatedpaper.

To obtain translucent paper, the paper base stock used is one which canbe impregnated with the aqueous basic solution of the olefin/maleiccopolymer composition. It is preferably a porous, waterleaf orslack-sized paper. It should have a relatively low air resistance,preferably below about 200 seconds/100 ml. of air (TAPPI T 460).However, papers having appreciable water resistance due to sizing or lowporosity may be impregnated by the wet pack method rather than by themore conven- =1 tional methods such as by the tub or size pressapplication. To obtain treated papers having good release properties itis desirable to keep most of the applied resin on the surface of thepaper or board. Thus the paper or board base stock used for this purposeshould be substantially resistant to penetration of the aqueous basicsolution of the resin by being either sized or of low porosity.

Grease proof paper can be obtained by this invention by impregnatingand/or coating any cellulosic base stock such as waterleaf, slack-sizedor hard-sized paper of high or low porosity. The base stock used mayhave pigments or fillers incorporated to obtain a treated paper whichretains a substantial amount of opacity. Papers obtained from any of theconventionally prepared pulps may be treated in accordance with thisinvention, e.g., sulfite, sulfate, rag stock papers, and paperscontaining pigment fillers such as clay, titanium dioxide etc.

As stated above, the alpha-olefin/rnaleic anhydride copolymer basicsolution used to treat the paper and which is improved by this inventionmay be one copolymer composition from one terminal alpha-olefin andmaleic anhydride; it may also be a copolymer composition prepared from amixture of terminal alpha-olefins and maleic anhydride; it may also be amixture of alphaolefin/maleic anhydride copolymers from the same ordiiferent alpha-olefins of different molecular weight such that theaverage molecular weight of the copolymer composition is from about 1000to about 10,000 as determined by the Mechrolab Osmometer method.

For this invention the higher alpha-olefins having from 6 to about 24 ormore carbon atoms are used to prepare the copolymer resin with maleicanhydride. The alphaolefin may be a substantially pure single terminalaliphatic alkene alpha-mono-olefin such as l-hexene, 3-methyl-l-pentene, 2-methyl-1-pentene, l-heptene, l-octene,2-methyl-1-octene, l-decene, l-undecene, l-dodecene, 1,tetradecene,l-pentadecene l-octadecene, l-eicosene, l-tetracosene, l-hexacosene, orit may be a particular distillation fractional cut or blend of variousstraight or branched'chained terminal alpha-mono-olefins. Preferredmixtures of alpha-olefins have from about 10 to about carbon atoms inthe olefin components. A particularly suitable blend of aliphaticalpha-mono-olefins of this type for use in preparing copolymers for userendering paper more translucent is a mixture of C to Calpha-mono-olefins. These olefins may be obtained from various sourcessuch as from the dehydration of fatty alcohols, from the polymerizationof ethylene and/ or propylene, from wax cracking products having lowdiolefin content, say, less than about 1 percent diolefin content.

Although for reasons of cost and availability we prefer to use maleicanhydride for reaction with the aliphatic alpha-olefins described above,it is contemplated that other related materials could also be used, butnot necessarily with the same advantageous results. Such materials wouldinclude maleic acid, fumaric acid, itaconic acid, citraconic acid, andtheir esters and anhydrides, such as the half-methyl ester of maleicanhydride.

The low molecular weight alpha-olefin/maleic anhydride copolymers may beprepared by any conventional solvent or non-solvent technique. Usuallythe alphaolefin and maleic anhydride are combined in proportions suchthat the maleic anhydride is in excess relative to the aliphatic olefin,e.g., in olefinzmaleic anhydride mole ratios of from 1:1 to about 1:19.When a solvent is used the copolymer product obtained usually has alittle higher proportion of maleic anhydride than the ratio charged. Forexample, in one run the olefinzmaleic anhydride charge ratio was about1:1.25. The ratio of the the copolymer obtained in xylene was 121.43.When a solvent is not used the copolymer obtained tends to have areacted mole ratio closer to the mole ratio of the charged olefin andmaleic anhydride reactants. We have found that for many applications itis not necessary to remove all of any excess olefin from the copolymerproduct before it is used in accordance with this invention. We havefound that up to about 6% and even higher amounts of olefin do notsubstantially impair the properties of the treated paper.

To obtain the low molecular weight desired for this invention it isconvenient to prepare the copolymer by conducting the reaction using adialkyl peroxide as an initiator or catalyst, a chain transfer agent anda reaction temperature suflicient to provide a reasonably shortinitiator or catalyst half-life so that the polymerization may takeplace in reasonably short periods of time. Generally with dialkylperoxides temperatures on the order of from about C. to about C. areused, although the temperature may vary from about 120 C. to about C.,depending upon the conditions used. With ditert-butyl peroxide asinitiator or catalyst, and xylene as chain transfer agent and solvent,temperatures of about 140155 C. are preferred with higher carbon contentolefins (over about 10 carbon atoms average). Reaction times will varyfrom about 0.5 hour to several hours depending upon the temperatureused, whether a solvent is used, etc.

In order to obtain a copolymer product which has a low enough viscosityfor use in accordance with this invention it is desirable to include inthe polymerization reaction mixture a chain transfer agent to controlthe average chain length of the copolymer. Any material which serves tolimit the growth of the polymer chain or to transfer polymerizingmoieties to monomers such that the average molecular weight range of theresulting copolymer product is from about 1000 to about 10,000 may beused. Examples of such chain transfer agents include cumene, thexylenes, alkyl and polyalkylbenzenes (e.g., diisopropylbenzene) whichcontain at least one hydrogen alpha to the benzene ring, dialkyl etherssuch as dimethyl ether, diethyl ether, and saturated aliphatic esters,ketones, aldehydes, mercaptan and other similar com-pounds having ahydrogen alpha to an activating group. Those in the art are aware ofchain transfer agents which may be used. Some chain transfer agentsserve as a diluent for the reaction mixture. However, the averagemolecular weight of the alpha-olefin/maleic anhydride copolymer may alsobe controlled in the absence of a chain transfer agent or diluent orsolvent by conducting the polymerization at higher temperatures, e.g.,160 C. to C. The polymerization should be conducted in an inertsubstantially oxygen free atmosphere. This may be done by conducting thepolymerization under an inert gaseous atmosphere such as nitrogen,carbon dioxide, or methane vapor, or refluxing solvent vapor.

When the polymerization is completed, the reaction mixture is usuallystripped to remove at least a part of any unreacted alpha-olefin ormaleic anhydride. Usually under the conditions used unreacted olefin ispresent to some extent. The reaction mixture is usually stripped orevaporated, preferably under reduced pressure to remove by-products suchas tertt-butanol when di-tert-butyl peroxide was used as the initiator,acetone, diluent or solvent, chain transfer agent etc., and someunreacted olefin. This is desirably accomplished at temperaturessufiiciently high to keep the crude product in the liquid state but nothigh enough to cause any substantial decomposition. Generallytemperatures of from about 160 C. to about 225 C., under vacuum down toabout 50 millimeters of Hg pressure or lower are used. The resin productwhich remains as residue may then be poured or otherwise emptied fromthe reaction vessel, and upon cooling to room temperature it solidifiesto a vitreous glassy material which can be crushed or ground easily toany convenient particle size.

These alpha-olefin/rnaleic anhydride copolymers are water soluble in thebasic side of .the pH range. Any

alkaline reacting material which produces water soluble salts, amides,or mixed amide-salts of the copolymer composition may be used to makeaqueous solutions of the copolymer. Examples include ammonia, ammoniumhydroxide, ammonium acetate, the hydroxide of alkali metals havingatomic weights of from about 22.9 to about 39, such as sodium hydroxide,sodium oxide, sodium carbonate, sodium propionate, potassium hydroxide,potassium carbonate, etc., so long as the concentration of the base usedis low enough to avoid precipitation of the polymer from aqueous media.Organic bases such as the heterocyclic amines e.g., pyridine,morpholine, picoline, the trialkylamines such as triethylamine,tributylamine, the alkylenediamines, and polyalkylenetriamines such asethylenediamine, diethylenetriamine, tripropylenetetramine may also beused. However, the preferred basic solubilizing agents are ammonia,ammonium hydroxide, and alkali metal hydroxide such as sodium hydroxideand mixtures of ammonium hydroxide with such alkali metal hydroxide.When ammonium hydroxide is used, the preferred practice is to slurry thepulverized solid resin into most (say, 75-90%) of the required amount ofwater to obtain the desired percent solids solution and while stirringadd the required amount of concentrated ammonium hydroxide to effectsolution by heating somewhat. A convenient amount of ammonium hydroxideto use is between about 0.5 and 0.6 ml. of concentrated (28%) ammoniumhydroxide per gram of resin used. The percent solids in the solutionscan be adjusted by adding water. The pH should be kept above about 7.5to 8.5 for the higher solids content to solutions to preventprecipitation.

When an alkali metal hydroxide is used as the basic solubilizing agentit is recommended that the pulverized resin be added to the heated(50-60 C.) aqueous solution of the base. We prefer to use about 0.15 toabout 0.30 g. of sodium hydroxide per gram of resin solids, althoughlower and higher amounts may be used. Gross excesses of sodiumhydroxide, however, should be avoided to prevent precipitation ofpolymer solids from the solution. When mixtures of sodium and ammoniumhydroxides are being used the polymer resin solids should be added tothe sodium hydroxide solution, and then aqueous ammonium hydroxide canbe added to complete solution formation.

The copolymer may also be used in the form of the aqueous basicsolutions of its partial amides, such as are formed by reacting thecopolymer with anhydrous ammonia, dialkylaminoalkylamines ordialkylaminoalkanols, its partial esters such as the one-half methyl orethyl esters of the alpha-olefin maleic anhydride copolymer, etc., andin the form of basic quaternary salts of the copolymer by reacting theamide formed from reaction of a dialkylaminoalkylamine with thecopolymer with quaternizing materials such as dimethyl sulfate and thelike.

The alkali metal bisulfite or alkali metal sulfite may be incorporatedinto the copolymer solution by any known method. The alkali metalbisulfite may be mixed with the dried pulverized-copolymer solids insuitable minor proportions before the copolymer is dissolved in theaqueous medium and the dried mixture of the copolymer and the alkalimetal bisulfite or sulfite may be added as such to the aqueous medium.Alternatively, the dried copolymer and the alkali metal bisulfite orsulfite salt may be added separately to the aqueous medium. It ispreferred to first dissolve a given weight amount of copolymer solids inan aqueous basic medium and then to add the minor proportion, preferablyfrom about 0.1% to about 5% of the salt based on the weight of polymerto the dissolved copolymer solution thus obtained.

The bisulfite and/or sulfite ions may be provided to the copolymersolution in any other convenient form also such as in the free acid formor as liquid S0 so long as a basic pH is maintained, or as the saltswith other metals such as lithium, rubidium, cesium, etc. so long as theamount of the salt used is not enough to precipitate the copolymer fromsolution. However, these materials are not preferred because ofhandling, availability, and cost considerations.

It is preferred to combine the alkali metal bisulfite or sulfite saltwith aqueous alkali metal hydroxide solutions of the copolymer to obtainoptimum color stability in the treated paper. It has been found,however, that the compositions of this invention dissolved in ammoniaand amine containing bases such as ammonium hydroxide possesssubstantial advantage over aqueous ammoniacal solutions of the copolymerwhich do not contain the alkali metal bisulfite or sulfite. Thecompositions of this invention so dissolved show substantial resistanceto liquid phase corrosion when the solution is held in copper basedalloy equipment. This is important since in the absence of the alkalimetal bisulfite or sulfite, the ammoniacal solution of the copolymerupon standing turns blue and when colored solutions applied to paper,the paper is discolored. When used to prevent discoloration ofammoniacal solution of the copolymer amounts ranging as low as about0.01 to 1% are generally sufiicient.

The aqueous basic copolymer composition solution thus obtained may beapplied to paper as such or there may be incorporated into the aqueoussolution. other additives or modifiers before it is applied to thepaper. Such materials which may be found desirable include antifoamingagents and/or defoaming agents, e.g., trialkyl phosphates such astributyl phosphate, sulfonated tallow waxes, liquid fatty acid mineraloils, as well as various commercial materials sold for theiranti-foaming or defoaming properties such as Hercules Defoamer 831,Nopco KFS, Napco 1497-V, General Electric Antifoam 60, and Dow CorningAntifoam A in amounts ranging from a few parts per million to about 0.5or 1 percent based on the weight of the copolymer resin of antifoamingor defoaming agent. The aqueous basic copolymer solutions may also beextended, blended with, or used to modify other paper chemicals beforebeing applied to paper. For example these copolymers either dry or intheir aqueous basic solutions may be blended with such materials asstarch, modified starches such as oxidized starch, enzyme convertedstarch, starch ethers, British gums, dextrins, and the like, casein etc.when it is desired to improve the water resistance of the coating onpaper. Amounts of such additional modifying agents may vary up to about98% by weight of the copolymer resin composition applied to paper in anaqueous basic medium.

When the aliphatic alkene alpha-olefin/maleic anhydride copolymer, assuch or in the form of its ammonium, or alkali metal salts, or itspartially amidated-partial salt form, such as the amidateid copolymerformed by treating the a-olefin/maleic .anhydride copolymer withanhydrous ammonia or a suitable amine and then dissolved in an aqueousmedium is extended with or blended into a starch for application topaper, the aqueous basic solution of the copolymer derivative may :beadded to the dry or wet starch before or after cooking. It may also beapplied to paper which has previously been treated with starchcompositions, For these applications of the copolymers applied to paperadmixed with starch it is preferred that the molecular weight of thecopolymer used be kept between about 1000 and 5000, although highermolecular weight copolymer materials up to about 10,- 000 may also beused if increased viscosities can be tolerated in the paper applicationprocedure used. The final starch-copolymer composition applied to pa ershould have neutral to basic pH, and should preferably be kept betweenabout 7 to about 10. The amount of starch with which the copolymers maybe blended or admixed for application to paper may vary widely dependingupon the purpose for which the copolymer is being used, the starch orstarch product with which the copolymer is to be admixed etc. Generally,starch alpha-olefin/rnaleic copolymer compositions containing from about1 percent to about 90 percent by weight of the copolymer, based on theweight of the starch, is sufficient for most applica-' tions in whichthe copolymer is applied to paper admixed with starch. When applied topaper admixed with starch to improve the water resistance thereof,maleic anhydride copolymers with alpha-olefins mixtures having from 6 toabout 10 carbons atoms are preferred, although the higher carbon contentolefins may also be used. For this purpose starch admixed with from toabout 15 percent, preferably about percent by weight of thealpha-olefin/maleic anhydride copolymer based on the weight of starchand applied to paper in an aqueous basic reacting system hassubstantially higher water resistance than paper treated with unmodifiedstarch. Improvements of up to 400 to 1000 percent in water resistance ofstarch on paper have been obtained in this man ner.

These alpha-olefin/maleic anhydride copolymers, and the ammonium, andalkali metal salts and ammoniatedamide derivatives thereof may also beused as binder or adhesive modifiers used in pigmented coatingcompositions for papers to be used in fine printing processes. Forexample, these copolymers are useful for modifying starch to improve theinsolubility characteristics of the starch which is often used as thebinder component of what is referred to in the art as a coating colorcomposition wherein pigments such as clay, calcium carbonate, and/ ortitanium dioxide, among many, are admixed with proportionately smalleramounts of starch, casein, or synthetic resin binders, usually on theorder of from about 5 to percent by weight, based on the weight of thetotal'pigment weight. The amount of the alpha-olefin/ maleic copolymerproduct, or derivative thereof, added to the starch used for any suchbinder purpose will vary depending on the degree of water resistancerequired and other factors such as the maximum permissible cost of thetreated paper thus obtained.

The modified aqueous basic solutions of alpha-olefin/ maleic anhydridecopolymer compositions of this invention may be applied to any paper,i.e., a prelaid web of paper, by any means known in the art. Applicationto a web of paper means application to paper which is formed in a web ona paper making machine. This distinguishes this method of applicationfrom the application to the paper pulp in the wet-end pulp treatingtechnique. For example, the aqueous solution of the resin may be appliedto the base sheet with an applicator, it may be sprayed on the paper, orthe paper as it is formed may be passed through the aqueous basic resinsolution at a speed adjusted to allow for the desired percent pickup ofresin solution. The resin solution may be of any concentrationsufficient to allow the paper to be impregnated, surface treated orcoated with the desired percentages of resin solution under theconditions applied. For most uses for which the treated paper isintended to be used it is preferred to use resin solutions having fromabout 10 percent to about 15 percent solids concentration, although forparticular uses, and for particular methods of application, solutionconcentrations having from about 1 percent to about percent solidsconcentration may be used. The amount of the aqueous basic copolymerapplied to the paper to be treated will vary depending upon the type ofpaper being treated and the object to be accomplished. Generally,amounts of the copolymer resin solution are used to provide the driedtreated paper with from about 0.001 percent to about 50 percent resinpickup, based on the weight of the untreated paper. For surfaceapplications and for coating thick substantially non-porous cellulosicpaper, the aqueous basic copolymer solution may be applied to thesurface of the paper in an amount sufiicient to provide the driedtreated paper with from about 0.1 to about 25 pounds of resin per 1000square feet of surface. When relatively porous papers are to be treatedto impregnate the interstices of the whole paper web or sheet it ispreferred to treat the paper with a suflicient amount of the copolymerresin solution to provide the dry treated paper having from about 0.1 toabout 30 percent resin pickup, based on the weight of the untreatedpaper.

The performances of paper treated with the aqueous basic solution of thealpha-olefin/maleic anhydride resin under various test conditions isfurther illustrated by the following detailed examples which are meantto illustrate how the polymers may be prepared, and properties of thetreated paper and are not intended as limitations on the scope of theinvention. The test methods used to determine the performance of thetreated papers are described below.

When paper is wetted and then dried, the expansioncontraction cyclecauses the resulting sheet to be cockled or wrinkled. To avoid cocklethe sheet must be dried under tension. The following treating method isa convenient way to impregnate sheets and dry them under tension. Theresulting sheets are cockle free.

The sheets were treated as follow to obtain uniform samples.

A. A rigid aluminum plate, larger in size than the sheet to be treated,is liberally coated with resin solution by means of a paint brush.

B. The sheet to be treated is applied to the prepared aluminum plate bycontacting one edge initially, and then the flexed sheet is rolledslowly into complete contact with the plate. Simultaneously more resinsolution is applied to the top of the sheet with the brush, usingtransverse strokes. Care is exercised to avoid uneven expansion andwrinkling of the sheet.

C. The wet paper sheet is covered with a sheet of polyethylene (2 mil)and the sandwich thus formed is passed through the rolls of a wringer.

D. The polyethylene sheet is immediately peeled off.

E. The sheet of impregnated paper is carefully peeled from the plate andlaid on TAPPI blotter paper. A small amount of glue, such a ElmersGlue-All, is placed on the circumference of an aluminum frame. With theglue side facing the impregnated sheet, the frame is laid on the sheetand pressed with mild pressure causing the sheet to adhere to the frame.(The frame has inside dimensions of 7 x 8" and outside dimensions of 9"x 10" and was designed to treat 9" x 10 sheets.)

F. The frame and treated paper are placed on a photo drier with thepaper side up and in contact with the canvas. Drying time is threeminutes at 205 F. (surface temperature of dryer).

G. The frame and paper are removed from the drier. The paper is then cutout of the frame and conditioned in a standard humidity-temperature roomovernight prior to testing. The frame is immediately soaked in Warmwater to loosen the paper adhering to the frame.

When sheets are treated by the wet pack method, treating solution isbrushed onto each sheet as it is stacked on the one under it. Excesssolution is left between each layer. The wet sheets are stored betweenglass plates, the entire unit being sealed in flexible plasticcontainers such as Saran Wrap to prevent drying of the treating solutionalong the edges. After the desired amount of wet packing (3 to 16 hours)the sheets are peeled from the stack and dressed through the Wringer anddried as described in the sequence above. The results reported here wereobtained on sheets wet packed for 16 hours.

TEST METHODS The test methods used to evaluate the base stock andtreated sheets are listed below along with explaining notes wherenecessary. Samples were conditioned according to TAPPI T402 m49 beforetesting.

A. Basis weighz.-This is determined by weighing 8 to 12 die cut sheetshaving dimensions of 6 X 7 inches or 4 X 7 inches. The results wereconverted to grams per square meter using information contained in TAPPIT410 s-61.

B. Tlz'ickness.TAPPI T411 m-44.

C. Percent pickup.-This was determined as follows:

Percent Pickup Weight of dried treated sheetweight of untreated sheetweight of untreated sheet D. Opacity-TAPPI T425 m-60 using a Bausch andLomb Opacimeter (Cat. #33-88-22) equipped with a white body having areflectance of 89%. Instead of reporting opacity as percent, it isreported in numerilcally equivalent points. This was done to avoidconfusion when using the terms opacity reduction and opacity increase.

E. Oil leakage.This is a modification of the method given in FederalSpec. UUP561e par. 4.3.5. The test sheet was placed between a sheet ofbond paper and a sheet of tablet paper. These were placed on a flatsurface under a pressure of 0.05 psi. The bond and tablet papers wereinspected after 48 hours to determine if the additive had migrated fromthe test sheet. Rating: pass or fail.

F. Oven aging tent-This test is described in UU-P-56le par. 4.3.3. Testsheets were hung in a Fisher Scientific Company forced draft Isotempoven for 72 hours. The oven temperature was 100 C. Opacity of the sheetwas determined before and after aging. Change in color of the sheet wasdetermined by visual inspection.

G. Fadeometer test (UU-P561e par. 4.3.6).Samples were exposed toultraviolet radiation for hours in a type FDA-R Fadeometer. Opacity ofthe test sheet was determined before and after exposure. Change in colorof the sheet was determined by visual inspection.

H. Folding resistance, M.I.T.M'0dified TAPPI T423 m-50.-The testspecimens were /2 X 6 inch strips cut with their long dimension inmachine direction. A one-kilogram sample loading was applied. Thenumbers given are double folds required to sever the specimen.

I. Tensile breaking strength-TAPPI T404 0s-6I.The

strips were one inch wide and cut in machine direction. The distancebetween clamps was 4 inches. Rate of jaw separation was 0.5 inch/minute.The instru ment was a table model Instron.

1. Air resistance(Gurley-Hill p0rosity)-TAPPI T460 m49.The time inseconds for passage of 100 ml. of air was measured.

K. Ink penetrati0n.-This was run at 35 C. with ink adjusted to a pH of1.5. Time, in seconds, for ink to penetrate through the sheet wasmeasured.

L. Pencil erasure-The paper is placed on a drawing board equipped with astandard drawing board cover and a pencil mark made with a blackgraphite 2H lead pencil. The mark is erased with an Eberhard Faber 101eraser. The paper is rated chiefly on mark removal; but also on lintingand smudging. 5 indicates complete mark removal with no linting o-rsmudging, 0 indicates a completely unsatisfactory result due to linting,smudging, or image retention.

M. Ink reception-With an Esterbrook pen equipped with a #2558 point andusing Sheaffers Permanent Blue Black #232 ink the test sheet is writtenupon. The marks are inspected for skipping and feathering. If neither ispresent the sheet is rated OK.

N. Ink eradication-The mark made with Sheaflers ink for the inkreception test is eradicated with Carters Rytofl. The eradicator isapplied to the mark and allowed to stand seconds. It is then blotted 10and allowed to stand an additional 20 seconds. The area is theninspected for mark removal. Complete removal i rated 5; completelyunsatisfactory removal is rated 0. When the test area had dried it iswritten upon with pen and ink; if no feathering occurs it is rated 5;extensive feathering is rated 0.

0. India ink recepti0n.-With a ruling pen, lines of black waterproof ink(Higgins India) are drawn on the sheet, The lines are inspected forskipping and feathering. If neither is present, the sheet is rated 6OK'!P. Internal tearing resistance-TAPPI T414 m49.-The long dimension of thesample was cut in machine direction .and then torn across the machinedirection.

Q. Stifiness.Stiflness was determined with a Gurley Stiffness Tester.The test sheet was flexed along the machine direction aXis.

Example 1 A mixed olefin/maleic anhydridc copolymer was prepared asfollows:

To a 22 liter flask equipped with stirrer, thermometer, refluxcondenser, nitrogen inlet tube, and additional funnel there was added4500 g. (20.0 moles) of a commercially available C14 C]8 mixed aliphaticalkene alphaolefin, and about one-half of 5309 g. (50.0 moles) of mixedXylenes. The flask wa purged with nitrogen while the mixture was heatedto about C. over about 1 hour. Then about one-half of 131.6 g. (0.9mole) of di-tert-butyl peroxide was added to the flask and addition of asolution of maleic anhydridc and the other half of the di-tertbutylperoxide dissolved in the other half of the Xylene was added from theaddition funnel over about 60 minutes while controlling the temperatureat from 140 C. to about C. Tert-butanol distillation was noted afterabout 45 minutes of addition. The mixture was held at 136-140 for 2hours and then Xylene was stripped out of the reaction mixture over a133 minute period at temperatures of from 138 C. up to about C. Thepressure was dropped to a final pressure of 40 mm. as the temperatureincreased. Total distillate including tert-butanol was 5530 g. Theviscous yellow resin polymer which remained as residue weighed 7015 g.was poured into storage containers. Upon cooling it solidified to ayellow-colored brittle glass. It was pulverized sufliciently to passthrough a 20 mesh screen. The copolymer had a specific viscosity of 0.24as measured on a 4% solution in methylethylketone at 25 C. The averagemolecular weight was 2095.

The liquid product obtained from these reactants before cooling had adensity of about 0.77 g./ml. (6.4 lbs/gal.) at 170 C. It had a meltingpoint of about 110 C. Approximate viscosities of the resin product atvarious temperatures are:

Temperature C.): Viscosity (stokes) The pulverized copolymer solid wasadded to a stirred, heated (S060 C.) aqueous solution of sodiumhydroxide containing about 0.23 g. of sodium hydroxide for each g. ofcopolymer resin. Heating was continued to 80 C. until all the resinparticles were dissolved. To portions of this solution there was added2% and 3%, based on the weight of the polymer solids, of sodiumbisulfite. When complete dissolution was effected, the aqueous basicsolution of the mixed alpha-olefin-maleic anhydridc copolymer containingthe sodium bisulfite was applied to a paper stock having thecharacteristics described in column 1 which was a control. The effectsof the chemical treatment are summarized in columns 2, 3, and 4.

Base Used for Solution Prep. C011- NaOH NaOH NaOH tro 1 Percent SodiumBisulfite 2 3 Percent Pickup of Dissolved So1id None 23. 4 24. 8 2A. 4Opacity, B /L points 75. 6 54. 2 53. 8 54. Basis Weight, g./m. 56.1 69.4 70.0 69. 9 (17 x 22500 sheets), lbs 14. 9 18. 18. 6 18.6 Thickness,mils 3. 60 3. 62 3. 71 3. 71 Air Resistance, sec/100 ml 13 74 83 79 InkPenetration, seconds 1 135 120 110 Tensile, MD lbs/inch widt 10. 2 24. 726. 6 27. 4 Internal Tear, CD, grams 59. 4 50. 3 51. 9 51. 4 MIT. Fold,MD, Double Folds.-- 58 40 49 53 Stiffness (Gurley), MD, mg 68. 1 95. 991. 7 98. 7 Oven Aging, 72 hours, 100 0.:

Opacity Increase, B/L points. 1. 0 2.2 1. 5 1. 5

Brightness Loss, points 8 0 13.0 11.0 10.5 Oil Leakage Pass Pass PassFadeonieter, Hours:

Opacity Increase, Points 0. 5 1. 5 1.0 1. 5

Color Change None None None None Pencil Erasure 5 5 5 Ink ReceptiolL OKOK OK Ink Eradication 5-3 5-2 5-1 India Ink Reception OK OK OK 1 Treatedwith distilled water.

These data show a substantial reduction in the amount of brightness lossupon accelerated oven aging when the paper is treated with aqueous basicsolutions of the copolymer containing a minor amount of the alkali metalbisulfite.

Example 2 To 10.0 g. portions of a mixed alpha-olefin/maleic anhydridecopolymer, prepared as described in Example 1, there was added 40-45 g.of distilled Water. While agitating the mixture ammonia solutionequivalent to 0.402 ml. of 28% ammonium hydroxide per gram of copolymerwas added. The mixture was stirred at room temperature for 10 minutesand then heated to 6070 C. and held at that temperature for minutes. ThepH of the aqueous ammoniacal copolymer solution was 7.7. The polymersolids content of the solution was adjusted to 15% polymer solidscontent.

Similar solutions to that above were prepared except that to one suchsolution there was added about 0.3 percent by weight of sodiumbisulfite, based on the weight of the polymer solids.

Such aqueous ammoniacal copolymer solutions, i.e., with and without thesodium bisulfite therein each of which solutions was originally clear,and slightly more yellow than distilled water were allowed to stand withpieces of copper wire immersed therein. After 3 days in contact withcopper, the aqueous ammoniacal copolymer solution containing the sodiumbisulfite had developed no more color than a similar ammoniacalcopolymer control solution not in contact with copper, whereas theaqueous ammoniacal copolymer solution which did not contain the sodiumbisulfite developed a definite blue color.

I claim:

1. A composition comprising (1) an aqueous basic solution of analiphatic alkene alpha-olefin/maleic anhydride copolymer having anolefin to maleic anhydride molar ratio of from about 1:1 to about 121.9and an average molecular weight of from about 1000 to about 10,000, thealpha-olefins having from 6 to about 24 carbon atoms, and (2) from about0.01 percent to about 5%, based on the copolymer content, of an alkalimetal salt of an anion selected from the group consisting of bisulfiteand sulfite.

2. A composition as described in claim 1 wherein in the aqueous basicsolution of the alpha-olefin/maleic anhydride copolymer (1) thealpha-olefin used to prepare the copolymer is a mixture of alpha-olefinshaving from about 10 to about 20 carbon atoms, and the basic materialused to solubilize the copolymer in water is selected from the groupconsisting of ammonia, ammonium hydroxide, alkali metal hydroxides andmixtures thereof, the alkali metal of said alkali metal hydroxideshaving an atomic weight of from about 22.9 to about 39, and the alkalimetal salt (2) is sodium bisulfite.

3. A composition as described in claim 2 wherein in the aqueous solutionof the alpha-olefin/maleic anhydride copolymer (1) the alpha-olefin usedto prepare the copolymer is a mixture of alpha-olefins having from about14 to about 18 carbon atoms, and the basic material used to solubilizethe copolymer in Water is an alkali metal hydroxide, the alkali metal ofwhich has an atomic weight of from about 22.9 to about 39, and thealkali metal salt (2) is sodium bisulfite.

4. Paper treated with a composition as described in claim 1.

5. Paper treated with a composition as described in claim 2.

6. Paper treated with a composition as described in claim 3.

No references cited.

MURRAY TILLMAN, Primary Examiner.

W. I. BRIGGS, SR., Assistant Examiner.

1. A COMPOSITION COMPRISING (1) AN AQUEOUS BASIC SOLUTION OF ANALIPHATIC ALKENE ALPHA-OLEFIN/MALEIC ANHYDRIDE COPOLYMER HAVING ANOLEFIN TO MALEIC ANHYDRIDE MOLAR RATIO OF FROM ABOUT 1:1 TO ABOUT 1:1.9AND AN AVERAGE MOLECULAR WEIGHT OF FROM AOUT 1000 TO ABOUT 10,000, THEALPHA-OLEFINS HAVING FROM 6 TO ABOUT 24 CARBON ATOMS, AND (2) FROM ABOUT0.01 PERCENT TO ABOUT 5%, BASED ON THE COPOLYMER CONTENT, OF AN ALKALIMETAL SALT OF AN ANION SELECTED FROM THE GROUP CONSISTING OF BISULFITEAND SULFITE.